sin十分之派乘cos五分之派怎么算

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sin十分之派乘cos五分之派怎么算

sin十分之派乘cos五分之派怎么算
sin十分之派乘cos五分之派怎么算

sin十分之派乘cos五分之派怎么算
sinπ/10*cosπ/5
=(cosπ/10*sinπ/10*cosπ/5)/(cosπ/10)
=(1/2sinπ/5cosπ/5)/(cosπ/10)
=(1/4sin2π/5)/sin(π/2-π/10)
=(1/4sin2π/5)/sin2π/5
=1/4